K60P100M100SF2RM Datasheet, PDF (505/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Chapter 22
External Watchdog Monitor (EWM)
22.1 Introduction
NOTE
For the chip-specific implementation details of this module's
instances see the chip configuration chapter.
The watchdog is generally used to monitor the flow and execution of embedded software
within an MCU. The watchdog consists of a counter that if allowed to overflow, forces an
internal reset (asynchronous) to all on-chip peripherals and optionally assert the RESET
pin to reset external devices/circuits. The overflow of the watchdog counter must not
occur if the software code works well and services the watchdog to re-start the actual
counter.
For safety, a redundant watchdog system, External Watchdog Monitor (EWM), is
designed to monitor external circuits, as well as the MCU software flow. This provides a
back-up mechanism to the internal watchdog that resets the MCU's CPU and peripherals.
The EWM differs from the internal watchdog in that it does not reset the MCU's CPU
and peripherals. The EWM if allowed to time-out, provides an independent EWM_out
pin that when asserted resets or places an external circuit into a safe mode. The CPU
resets the EWM counter that is logically ANDed with an external digital input pin. This
pin allows an external circuit to influence the reset_out signal.
22.1.1 Features
Features of EWM module include:
• Independent LPO clock source
• Programmable time-out period specified in terms of number of EWM LPO clock
cycles.
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
505